JavaAlgorithms/Ciphers/Caesar.java

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package Ciphers;
import java.util.Scanner;
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/**
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* A Java implementation of Caesar Cipher. /It is a type of substitution cipher in which each letter
* in the plaintext is replaced by a letter some fixed number of positions down the alphabet. /
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*
* @author FAHRI YARDIMCI
* @author khalil2535
*/
public class Caesar {
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/**
* Encrypt text by shifting every Latin char by add number shift for ASCII Example : A + 1 -> B
*
* @return Encrypted message
*/
public static String encode(String message, int shift) {
StringBuilder encoded = new StringBuilder();
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shift %= 26;
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final int length = message.length();
for (int i = 0; i < length; i++) {
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// int current = message.charAt(i); //using char to shift characters because ascii
// is in-order latin alphabet
char current = message.charAt(i); // Java law : char + int = char
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if (IsCapitalLatinLetter(current)) {
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current += shift;
encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters
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} else if (IsSmallLatinLetter(current)) {
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current += shift;
encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters
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} else {
encoded.append(current);
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}
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}
return encoded.toString();
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}
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/**
* Decrypt message by shifting back every Latin char to previous the ASCII Example : B - 1 -> A
*
* @return message
*/
public static String decode(String encryptedMessage, int shift) {
StringBuilder decoded = new StringBuilder();
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shift %= 26;
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final int length = encryptedMessage.length();
for (int i = 0; i < length; i++) {
char current = encryptedMessage.charAt(i);
if (IsCapitalLatinLetter(current)) {
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current -= shift;
decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters
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} else if (IsSmallLatinLetter(current)) {
current -= shift;
decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters
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} else {
decoded.append(current);
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}
}
return decoded.toString();
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}
/**
* @return true if character is capital Latin letter or false for others
*/
private static boolean IsCapitalLatinLetter(char c) {
return c >= 'A' && c <= 'Z';
}
/**
* @return true if character is small Latin letter or false for others
*/
private static boolean IsSmallLatinLetter(char c) {
return c >= 'a' && c <= 'z';
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Please enter the message (Latin Alphabet)");
String message = input.nextLine();
System.out.println(message);
System.out.println("Please enter the shift number");
int shift = input.nextInt() % 26;
System.out.println("(E)ncode or (D)ecode ?");
char choice = input.next().charAt(0);
switch (choice) {
case 'E':
case 'e':
System.out.println(
"ENCODED MESSAGE IS \n" + encode(message, shift)); // send our function to handle
break;
case 'D':
case 'd':
System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));
default:
System.out.println("default case");
}
input.close();
}
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}